1. Field of the Invention
This invention relates generally to an arrangement for coupling two sections of pipe, and more specifically, this invention relates to a coupling for mechanically joining two sections of pipe which may carry fluids at relatively high pressures while electrically insulating the sections of pipe from one another.
2. Description of the Prior Art
In coupling pipes that are to carry fluids under relatively high pressures, such as in gas and oil transmission lines, it is necessary that a good mechanical joint be combined with a good seal to prevent leakage of the fluid. Also, as the pipes being coupled are normally electrically conductive metallic members, it is desirable to electrically insulate the sections of pipe being coupled, in order to prevent formation of an electrical current flow path from one section of pipe to the other.
One of the best, if not the best, high pressure insulated couplings found in the prior art is that manufactured by the company to which the present application is assigned. In this device, a heavy wall seamless steel tubing provides a coupling body. Threads are welded or swaged to the outer surface of the coupling body at each end thereof. A polypropylene lining is located along the inner surface of the coupling body. A plastic sliding stop of a so called "waffle" design is utilized to slide within the polypropylene lining and separate the ends of the sections of pipe being joined with an insulating layer. Threaded coupling nuts are located at each end of the coupling to engage the threads on the coupling body and compress appropriate gaskets. One of the gaskets includes an exposed metallic beaded ring to provide a bond between the coupling body and that section of pipe, while the other gasket is formed entirely of rubber and overlaps the polypropylene lining to provide complete insulation at that end of the coupling body.
While this prior art coupling has shown great utility and has performed very well in use, it has some disadvantages in that it is relatively large and relatively expensive. As a result, although no other prior art coupling can compare in terms of performance and reliability, there are some areas in which improvements can be made.